The microcellular materials according to the invention are porous monoliths of centimetric size, the porosity of which is characterized by the presence of spherical cavities also called “cells”, which have a diameter situated generally between 1 and 100 μm, in particular from approximately 2 μm to approximately 50 μm, and preferably from approximately 5 μm to approximately 20 μm. These cells are generally all interconnected with their close neighbours by apertures or “windows” of a smaller size than their own size. These interconnecting windows have variable dimensions and have a diameter from approximately 0.5 to approximately 10 μm in particular from approximately 50 nm to approximately 1000 nm, and preferably from approximately 250 nm to approximately 500 nm.
The interconnected microcellular materials according to the invention have a particularly low density of 0.02 to 0.2 g·cm−3.
The existing interconnected microcellular materials are generally obtained by the polyHIPE (Polymerization of a High Internal Phase Emulsion) method. Such materials are, for example, described in patent application FR 2 932 184.
The polyHIPE method consists of the polymerization of a highly concentrated emulsion which is composed of an internal dispersed phase the volume percent of which is greater than that of the external dispersion phase. The volume percent of the internal dispersed phase must theoretically be greater than or equal to 74% with respect to the total volume of the emulsion. This threshold of 74% corresponds to the maximum volume occupied by uniform spherical drops of the internal dispersed phase and arranged so that they do not undergo deformation. Beyond 74%, the drops are compressed against each other. In the case of an emulsion exhibiting a wide drop size distribution (namely a polydisperse emulsion), the threshold for obtaining, after polymerization, an interconnected porous structure can be less than the theoretical value of 74%.
The external dispersion phase of the polyHIPE method constitutes the continuous phase and comprises mainly monomers capable of polymerizing as well as a surfactant in solution in a solvent. The internal dispersed phase is mainly constituted by a solvent that is immiscible with the monomers and/or with the solvent of the continuous phase.
After polymerization and elimination of the solvent from the internal dispersed phase, interconnected microcellular materials are obtained.
In view of their structure and their physical properties, interconnected microcellular materials are the subject of increasing interest and their use has been proposed in many fields, among which are the manufacture of disposable absorbent articles, thermal, acoustic, electrical or mechanical insulation articles, membranes, filters or also supports for inks, colorants and catalysts.
However, the interconnected microcellular materials described to date are obtained from polymerizable precursors mainly of petroleum origin or of synthetic origin, i.e. from non-plant and non-renewable raw materials. In the light of diminishing world oil reserves, the valorization of renewable materials to replace them has become a priority.
A need therefore exists to have available interconnected microcellular materials prepared from renewable raw materials as well as methods for the preparation of these materials, in particular the polyHIPE methods, which use renewable raw materials. It is also important to promote a sustainable development approach by valorizing industrial waste, without a negative impact on other priority uses of such resources, such as human or animal food, and without additional environmental impact.